“He’s leaving tomorrow morning,” a source tells Us Weekly. “It wasn’t set in stone because William needed to clear the week of work first.”

On Wednesday, the 30-year-old Duchess flew first class to St. Lucia with her parents, Mike and CaroleMiddleton and her siblings, Pippa and James Middleton. After arriving in the Caribbean, the family made their way to the ultra-private island of Mustique, where they will celebrate Carole’s 57th birthday (her actual birthday is January 31).

This isn’t the first time the Middletons took Mustique. The family, sans Kate, vacationed there last August.

This vacation may be the last bit of R&R that the Duke of Cambridge, 29, sees for awhile. The Prince, who is a search-and-rescue co-pilot for the Royal Air Force, is scheduled to be deployed to the Falkland Islands, which is the center of fresh tension between Great Britain and Argentina, next month.